Type checking and conversion in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What function in R checks the type of an object?

The typeof() function returns the internal type or storage mode of any R object.

beginner

How do you convert a numeric value to a character string in R?

Use the as.character() function to convert numeric values to character strings.

beginner

What does the is.numeric() function do in R?

It checks if an object is of numeric type and returns TRUE if it is, otherwise FALSE.

intermediate

How can you convert a character vector to a factor in R?

Use the as.factor() function to convert a character vector into a factor, which is useful for categorical data.

intermediate

What happens if you try to convert a non-numeric character string to numeric using as.numeric()?

R returns NA with a warning because the string cannot be interpreted as a number.

Which function checks if an object is a character vector in R?

A is.character()

B as.character()

C typeof()

D is.numeric()

The is.character() function returns TRUE if the object is a character vector.

What does typeof(42L) return in R?

A "integer"

B "double"

C "numeric"

D "character"

The suffix L makes 42 an integer, so typeof(42L) returns "integer".

Which function converts a factor back to a character vector?

A is.factor()

B as.factor()

C as.character()

D typeof()

Use as.character() to convert factors to character vectors.

What will as.numeric("abc") return?

A An error stopping the program

B 0

C "abc"

D NA with a warning

R returns NA and a warning because "abc" cannot be converted to a number.

Which function tells you the class of an object in R?

A typeof()

B class()

C is.numeric()

D as.character()

class() returns the object's class, which is a higher-level description than typeof().

Explain how to check the type of a variable and convert it to another type in R.

Think about functions that check type and those that change type.

Describe what happens when you try to convert a non-numeric string to numeric in R and how to handle it.

Consider what R returns and how you might check for conversion success.

Practice

1. Which function in R checks if a variable is of numeric type?

easy

A. as.character()

B. as.numeric()

C. is.character()

D. is.numeric()

Solution

1. Step 1: Understand type checking functions

   Functions starting with is. check the type of a variable.

2. Step 2: Identify the correct function for numeric check

   is.numeric() returns TRUE if the variable is numeric.

3. Final Answer:

   is.numeric() -> Option D

4. Quick Check:

   Type check numeric = is.numeric() [OK]

Hint: Use is.type() to check type, as.type() to convert [OK]

Common Mistakes:

• Confusing is.numeric() with as.numeric()
• Using as.character() to check type
• Using is.character() for numeric check

2. Which of the following is the correct way to convert a character vector c("1", "2", "3") to numeric in R?

easy

A. is.numeric(c("1", "2", "3"))

B. as.numeric(c("1", "2", "3"))

C. as.character(c(1, 2, 3))

D. is.character(c(1, 2, 3))

Solution

1. Step 1: Identify conversion functions

   as.numeric() converts data to numeric type.

2. Step 2: Apply conversion to character vector

   Using as.numeric(c("1", "2", "3")) converts strings to numbers 1, 2, 3.

3. Final Answer:

   as.numeric(c("1", "2", "3")) -> Option B

4. Quick Check:

   Convert char to numeric = as.numeric() [OK]

Hint: Use as.numeric() to convert strings to numbers [OK]

Common Mistakes:

• Using is.numeric() instead of as.numeric()
• Trying to convert numeric to character for numeric conversion
• Confusing is.character() with conversion functions

3. What will be the output of the following R code?

vec <- c("10", "20", "30")
num_vec <- as.numeric(vec)
is.numeric(num_vec)

medium

A. TRUE

B. FALSE

C. Error

D. NA

Solution

1. Step 1: Convert character vector to numeric

   as.numeric(vec) changes strings "10", "20", "30" to numbers 10, 20, 30.

2. Step 2: Check if converted vector is numeric

   is.numeric(num_vec) returns TRUE because num_vec is numeric.

3. Final Answer:

   TRUE -> Option A

4. Quick Check:

   as.numeric() converts, is.numeric() confirms [OK]

Hint: as.numeric() converts, is.numeric() checks type [OK]

Common Mistakes:

• Expecting FALSE because original was character
• Thinking as.numeric() returns character
• Confusing is.numeric() with as.numeric()

4. Identify the error in the following R code snippet:

val <- "123abc"
num_val <- as.numeric(val)
print(num_val)

medium

A. No error, prints 123

B. Syntax error due to quotes

C. Prints NA with a warning

D. Prints 0 without warning

Solution

1. Step 1: Attempt to convert mixed string to numeric

   as.numeric("123abc") cannot convert because of non-numeric characters.

2. Step 2: Result of conversion

   It returns NA and shows a warning about NAs introduced by coercion.

3. Final Answer:

   Prints NA with a warning -> Option C

4. Quick Check:

   Invalid numeric conversion = NA + warning [OK]

Hint: Invalid numeric strings convert to NA with warning [OK]

Common Mistakes:

• Expecting partial numeric conversion
• Ignoring warning messages
• Assuming syntax error due to quotes

5. You have a list lst <- list("5", 10, "abc", "15.5"). Which R code correctly converts all elements to numeric, replacing non-convertible values with 0?

hard

A. sapply(lst, function(x) if(is.na(as.numeric(x))) 0 else as.numeric(x))

B. sapply(lst, function(x) as.numeric(x))

C. sapply(lst, function(x) if(is.na(as.numeric(x))) as.numeric(x) else 0)

D. sapply(lst, function(x) if(is.numeric(x)) x else 0)

Solution

1. Step 1: Convert each element to numeric and check for NA

   Use as.numeric(x) inside a function and check if result is NA.

2. Step 2: Replace NA with 0, else keep numeric value

   If as.numeric(x) is NA, return 0; otherwise return the numeric value.

3. Final Answer:

   sapply(lst, function(x) if(is.na(as.numeric(x))) 0 else as.numeric(x)) -> Option A

4. Quick Check:

   Replace NA with 0 using conditional inside sapply [OK]

Hint: Use is.na(as.numeric(x)) to detect and replace [OK]

Common Mistakes:

• Not checking for NA after conversion
• Replacing numeric values incorrectly
• Confusing condition logic in if-else